inherited DataGrid failed to render

[Frank]

Hi all,

I want to derive a class from DataGrid so that I can have
a label on the top.
But when I tried to add the control to my form, I got an
error "Specified cast is not valid" on the line:
base.Render(w); inside the Render function.

Thanks a lot.
Frank

Here is my simple code.
private void Page_Load(object sender, System.EventArgs e)
{

Grid2 g=new Grid2();
this.Form1.Controls.Add(g);
}

public class Grid2 : System.Web.UI.WebControls.DataGrid{
System.Web.UI.WebControls.Label label=new Label();
protected override void OnInit(EventArgs e) {
this.label.Text="label 1";
this.Controls.Add(this.label);
}
protected override void Render(HtmlTextWriter w) {
this.label.RenderControl(w);
base.Render(w);

}
}